Aberystwyth harbour trap Swell Statistics, Autumn: Surf with Light or Offshore Winds
This image shows only the swells directed at Aberystwyth harbour trap that coincided with light winds or offshore conditions over a normal northern hemisphere autumn and is based upon 7249 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. Green and yellow show increasing swell sizes and red illustrates biggest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the most common swell direction, shown by the largest spokes, was SW (which was the same as the prevailing wind direction). The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 4% of the time, equivalent to 4 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal northern hemisphere autumn but 3% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 3%, equivalent to (3 days). Taking into account the ratio of these swells that coincided with predicted offshore winds, and given the fact that Aberystwyth harbour trap is slightly protected from open water swells, we think that that clean surf can be found at Aberystwyth harbour trap about 4% of the time and that surf is spoilt by onshore wind 26% of the time. This is means that we expect 27 days with waves in a typical northern hemisphere autumn, of which 4 days should be surfable.
IMPORTANT: Beta version feature! Swell heights are open water values from NWW3. There is no attempt to model near-shore effects. Coastal wave heights will generally be less, especially if the break does not have unobstructed exposure to the open ocean.